1. Field of the Invention
The present invention relates to a linear actuator for reciprocating a slide table along an axial direction of a main cylinder body by introducing a pressurized fluid through a fluid inlet/outlet port.
2. Description of the Related Art
Linear actuators, for example, fluid pressure-operated cylinders have been hitherto used as means for transporting workpieces or the like. The linear actuator comprises a slide table which is linearly reciprocated along a main cylinder body so that a workpiece placed on the slide table is transported.
A linear actuator concerning a conventional technique is based on a technical concept disclosed in, for example, Japanese Laid-Open Utility Model Publication No. 5-42716. As shown in FIGS. 39A and 39B, the fluid pressure-operated cylinder 1 comprises a main cylinder body 2 and a guide rail 3 formed to protrude on an upper surface of the main cylinder body 2 along a longitudinal direction.
The fluid pressure-operated cylinder 1 includes a slide table 4 which is slidably displaceable along the guide rail 3 in accordance with a displacement action of a piston accommodated in a cylinder chamber. Ball-circulating holes (not shown) for rolling a plurality of unillustrated bearing balls are defined in the slide table 4 along the longitudinal direction of the slide table 4. Screw holes 5a to 5d for attaching a workpiece are defined through an upper surface of the slide table 4. A pair of attachment holes 6a, 6b for attaching and securing the main cylinder body 2 to another member (not shown) are defined at corners located diagonally on the main cylinder body 2.
In the case of the fluid pressure-operated cylinder 1 shown in FIGS. 39A and 39B, the width L of the main cylinder body 2 in its transverse direction is represented by L.apprxeq.L.sub.1 +(L.sub.2 .times.2) (L.sub.1 : width of the guide rail 3, L.sub.2 : diameter of the attachment holes 6a, 6b). Namely, the width L of the main cylinder body 2 approximately has a value obtained by adding the width L.sub.1 of the guide rail 3 to the diameters L.sub.2 of the two attachment holes 6a, 6b. In this arrangement, it is impossible to reduce the width L.sub.1 of the guide rail 3 because the rigidity of the slide table 4 is decreased. Consequently, the width L of the main cylinder body 2 has a value obtained by adding the width L.sub.1 of the guide rail 3 to the diameters L.sub.2 of the attachment holes 6a, 6b.
As described above, in the case of the fluid pressure-operated cylinder 1 concerning this conventional technique, the width L of the main cylinder body 2 cannot be reduced because of the influence of the width L.sub.1 of the guide rail 3. As a result, the fluid pressure-operated cylinder 1 has an inconvenience in that the entire cylinder apparatus fails in achievement of a compact size and a light weight.
A linear actuator concerning another conventional technique is based on a technical concept disclosed in, for example, Japanese Laid-Open Utility Model Publication No. 6-43302. As shown in FIG. 40, the fluid pressure-operated cylinder 7 comprises a cylinder body 8 and a table 10. The cylinder body 8 includes a cylinder chamber formed therein. The table 10 is movable along an axial direction of the cylinder body 8 in accordance with a guiding action of a linear guide 9 secured to an upper surface of the cylinder body 8. A first protrusion 11 is formed to protrude upwardly at one end located in a transverse direction of the cylinder body 8. Second and third protrusions 12, 13 are formed to protrude laterally on one side surface located in the transverse direction of the table 10 so that the first protrusion 11 is interposed between the second and third protrusions 12, 13.
In this arrangement, bolts 14, 15, which are screwed into the second and third protrusions 12, 13 respectively, abut against the first protrusion 11. Thus terminal positions of movement of the table 10 are regulated. The amount of movement of the table 10 is adjusted by adjusting the screwing amounts of the bolts 14, 15.
However, in the case of the fluid pressure-operated cylinder 7 concerning the another conventional technique shown in FIG. 40, the first to third protrusions 11, 12, 13, which function to adjust the amount of movement of the table 10, are formed to protrude outwardly along the transverse direction of the fluid pressure-operated cylinder 7. Accordingly, the fluid pressure-operated cylinder 7 has an inconvenience in that it is impossible to reduce with width L in the transverse direction of the fluid pressure-operated cylinder 7 including the table 10, and the entire cylinder apparatus fails in achievement of a compact size and a light weight, in the same manner as the fluid pressure-operated cylinder 1 concerning the foregoing conventional technique.
Further, in the case of the fluid pressure-operated cylinders 1, 7 concerning the conventional techniques shown in FIGS. 39A, 39B, and 40, the width L.sub.1 of the guide rail 3 and the width L.sub.2 of the linear guide 7 are formed to be relatively small as compared with widths L of the main cylinder bodies (cylinder bodies) 2, 8. For this reason, an inconvenience arises in that linear accuracy of the slide tables 4, 10 is deteriorated by loads applied horizontally to the slide table (table) 4, 10.
A linear actuator concerning still another conventional technique is based on a technical concept disclosed in, for example, Japanese Laid-Open Utility Model Publication No. 6-47708. As shown in FIGS. 41 and 42, the fluid pressure-operated cylinder 16 comprises a main cylinder body 17 including a linear rolling bearing 16a formed to protrude at its central portion, and a table 18 which is linearly reciprocatable in accordance with a guiding action of the linear rolling bearing 16a.
A permanent magnet 18a is secured to one side surface of the table 18. A guide rail 18c is fastened to one side surface of the main cylinder body 17 by the aid of a pair of screws 18b, 18b. An elongated groove 18d is formed in the guide rail 18c along its axial direction. The position of the table 18 is detected by sensing a magnetic action of the permanent magnet 18a by using a magnetic proximity switch 19 installed at a predetermined position in the elongated groove 18d.
A pair of fluid pressure supply ports 19a, 19a (one of them is not illustrated), which are used to screw unillustrated tube fittings thereinto and connect piping tubes (not shown), are formed at positions close to the guide rail 18c on one side surface of the main cylinder body 17.
However, in the case of the fluid pressure-operated cylinder 16, the guide rail 18c, to which the magnetic proximity switch 19 is installed, is fastened to the one side surface of the main cylinder body 17 by means of the screws 18d, 18d. Accordingly, it is necessary to form screw holes for screwing the screws 18d, 18d thereinto, on the side surface of the main cylinder body 17. Therefore, it is necessary that the thickness M between an inner wall surface of the cylinder chamber and an outer wall surface of the main cylinder body 17 (see FIG. 42) is formed to be thick, in order to bore the screw holes. As a result, it is impossible to reduce the width W in the transverse direction of the main cylinder body 17. Thus a difficulty arises in that it is impossible to allow the entire apparatus to have a compact size and a light weight.
In the case of the fluid pressure-operated cylinder 16 concerning the conventional technique, an inconvenience arises in that the guide rail 18c, which protrudes outwardly as compared with the fluid pressure supply ports 19a, 19a, is obstructive, and thus the piping operation becomes complicated when the tube fittings are screwed in order to connect the piping tubes to the fluid pressure supply ports 19a, 19a of the main cylinder body 17.